Data storage device reading data from magnetic tape in forward and reverse direction

ABSTRACT

A data storage device is disclosed comprising at least one head configured to access a magnetic tape. The head is used to write contiguously to the magnetic tape a first preamble, followed by a first sync mark, followed by symbols of a first data sector, followed by a second sync mark, followed by a second preamble, followed by a third sync mark, followed by symbols of a second data sector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 63/071,007, filed on Aug. 27, 2020, which is herebyincorporated by reference in its entirety.

BACKGROUND

Conventional tape drive storage systems comprise a magnetic tape woundaround a dual reel (reel-to-reel cartridge) or a single reel (endlesstape cartridge), wherein the reel(s) are rotated in order to move themagnetic tape over one or more transducer heads during write/readoperations. The format of the magnetic tape may be single track ormultiple tracks that are defined linearly, diagonally, or arcuate withrespect to the longitudinal dimension along the length of the tape. Witha linear track format, the heads may remain stationary relative to thelongitudinal dimension of the tape, but may be actuated in a lateraldimension across the width of the tape as the tape moves past the heads.With a diagonal or arcuate track format, the heads may be mounted on arotating drum such that during access operations both the heads and tapeare moved relative to one another (typically in opposite directionsalong the longitudinal dimension of the tape).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a data storage device according to an embodimentcomprising at least one head configured to access a magnetic tape.

FIG. 1B is a flow diagram according to an embodiment wherein at leasttwo data sectors are written contiguously including an interveningpreamble that may be used to sync to a first data sector in a reversedirection or to a second data sector in a forward direction.

FIG. 1C shows a data track format according to an embodiment wherein async mark is used to synchronize to the symbols of a data sector.

FIG. 1D shows a data track format wherein data sectors are writtencontiguously by writing a sync/preamble/sync sequence between the datasectors to facilitate forward and reverse reading.

FIG. 1E shows a data storage device comprising a cartridge assemblycomprising a magnetic tape, and a tape drive assembly configured toaccess the magnetic tape.

FIG. 2 shows a prior art data track format wherein async/preamble/gap/preamble/sync sequence is written between the datasectors.

FIG. 3A shows a data track format according to an embodiment wherein async/preamble/sync sequence is written between the data sectors whichimproves format efficiency.

FIG. 3B shows a data track format according to an embodiment wherein anold data sector is overwritten with a new data sector by splicing intothe sync/preamble/sync sequence of the old data sector.

FIG. 3C shows a data track format according to an embodiment wherein anold data sector is overwritten with a new data sector by overwriting atleast part of the ending sync mark of the preceding data sector.

FIG. 3D shows a data track format according to an embodiment wherein awrite operation is terminated by splicing into the sync/preamble/syncsequence of the following data sector.

FIG. 3E shows a data track format according to an embodiment wherein awrite operation is terminated by leaving a gap instead of writing anending sync mark.

DETAILED DESCRIPTION

FIGS. 1A and 1B show a data storage device according to an embodimentcomprising at least one head 2 configured to access a magnetic tape 4.The data storage device further comprises control circuitry 6 configuredto execute the flow diagram of FIG. 1B, wherein the head is used towrite contiguously a first preamble, followed by a first sync mark arewritten (block 8), followed by symbols of a first data sector (block10), followed by a second sync mark, followed by a second preamble,followed by a third sync mark (block 12), followed by symbols of asecond data sector (block 14).

In the embodiment of FIG. 1A, the data storage device comprises anembedded magnetic tape 4 installed into a tape drive assembly which, inone embodiment, may be the same form factor as a conventional diskdrive. In another embodiment shown in FIG. 1E, the magnetic tape 4 maybe housed in a cartridge assembly 3 that is inserted into (and ejectedfrom) a tape drive assembly 5 similar to a conventional tape drivemanufactured under the Linear Tape-Open (LTO) standard. In oneembodiment, the tape drive assembly 5 comprises the head 2 configured toaccess the magnetic tape 4, and the control circuitry 6 configured toexecute the flow diagram of FIG. 1B.

FIG. 1C shows a data track format according to an embodiment whereinwhen writing a data sector, a preamble 16 is written by writing apredetermined number of magnetic transitions at any suitable frequencywhich facilitates synchronizing timing recovery when reading the datasector. A sync mark 18 is written following the preamble 16, wherein thesync mark 18 is used to synchronize to the symbols of the data sectorwhen reading the data sector. The sync mark 18 may consist of anysuitable pattern, wherein in one embodiment the sync mark 18 consists ofa pattern that maximizes the probability of accurate detection relativeto the preamble and the first symbol of the data sector. In oneembodiment, each symbol of the data sector represents a symbol of anerror correction code (ECC) codeword, such as a low density parity check(LDPC) codeword.

FIG. 1D shows a data track format wherein each data sector is writtenwith a beginning sync mark 18A used to symbol synchronize to the datasector while reading the data sector in a forward direction, and anending sync mark 18B used to symbol synchronize to the data sector whilereading the data sector in a reverse direction. In one embodiment, thebeginning sync mark 18A and the ending sync mark 18B may consist of thesame pattern, or in alternative embodiment the sync marks may consist ofdifferent patterns relative to one another.

FIG. 2 shows a prior art data track format wherein a:

-   -   sync/preamble/gap/preamble/sync        sequence is written between the data sectors. That is, each data        sector is written with a beginning and ending sync mark to        facilitate synchronizing to the data sector while reading in the        forward or reverse direction. However, the prior art data track        format of FIG. 2 is inefficient for at least two reasons: first,        each data sector is written with a beginning and ending preamble        field; and second, there is a gap left between the data sectors.        In contrast, FIG. 3A shows an embodiment of a data track wherein        a:    -   sync/preamble/sync        sequence is written between the data sectors without leaving a        gap between the data sectors (i.e., the data sectors are written        contiguously). This data track format improves the format        efficiency as compared to the prior art format of FIG. 2 by        obviating the gap field as well as obviating the extra preamble        field. Because the data sectors are written contiguously, the        preamble 20 in the example of FIG. 3A may be used to synchronize        timing recovery when reading data sector 22 in the forward        direction, or when reading data sector 24 in the reverse        direction. That is, a single preamble may be used to synchronize        timing recovery for two data sectors instead of having a        dedicated beginning/ending preamble for each data sector as in        the prior art data track format of FIG. 2.

In one embodiment, it may be desirable to overwrite a previously writtendata sector (or data sectors) by splicing into a sequence of datasectors that were written contiguously as in the data track format ofFIG. 3A. In an embodiment shown in FIG. 3B, the previously written datasector 22 of FIG. 3A is overwritten by a new data sector 26 byoverwriting at least part of preamble 20 with a new preamble 28(followed by the beginning sync mark for the new data sector 26). Thatis, the new data sector is “splice” written so that the new preamble 28may be used to symbol synchronize the new data sector 26 during aforward read as well as symbol synchronize to the preceding data sector24 during a reverse read. In one embodiment, writing the new preamble 28may result in a discontinuity between the new preamble and the endingsync mark of the preceding data sector 24. This discontinuity may resultin a small frequency and/or phase shift in the read signal when readingthe preamble 28 and the ending sync mark during a reverse read of thedata sector 24. In one embodiment, the small frequency and/or phaseshift in the read signal may be compensated in any suitable manner, forexample, by employing a suitable interpolated timing recovery configuredto search for the correct sampling frequency and/or phase whenattempting to detect the ending sync mark of the data sector 24. Forexample, in one embodiment the read signal samples of at least theending sync mark may be buffered and then processed iteratively using aninterpolated timing recovery which incrementally adjusts the samplingfrequency and/or phase of the read signal samples until the ending syncmark is successfully detected.

In another embodiment shown in FIG. 3C, when overwriting the previouslywritten data sector 22 of FIG. 3A the preamble 28 may overwrite at leastpart of the ending sync mark of the preceding data sector 24. In thisembodiment, the ending sync mark of the preceding data sector 24 isconverted into a gap field which helps ensure the preamble 28 of datasector 26 does not overwrite the end of the data sector 24 due to timingrecovery error. In this embodiment, converting the ending sync mark ofdata sector 24 into a gap field means the ending sync mark may no longerbe available to synchronize to the data sector 24 during a reverse read.In one embodiment, when the ending sync mark of data sector 24 becomesundetectable, other techniques may still be employed to read the datasector 24 in the reverse direction, such as by using an intermediatesync mark recorded within the data sector 24 (and erasing theintervening symbols), or performing reverse synchronization from anintervening or even the beginning sync mark of data sector 24.

FIG. 3D shows an embodiment wherein the end of a newly written datasector 26 may be spliced together with the preamble of a previouslywritten following data sector. In this embodiment, the ending sync markof the new data sector 26 may overwrite the ending sync mark of an olddata sector 24. Similar to the embodiment described above, splicing theending sync mark of data sector 26 with a previously written preamblemay result in a discontinuity in the sampling frequency and/or phasewhen reading the data sector 26 in the reverse direction. As describedabove, the discontinuity may be compensated by synchronizing thebuffered read signal samples using interpolated timing recovery.

In one embodiment, timing recovery error may prevent the accuratesplicing of the ending sync mark of a newly written data sector 26 withthe previously written preamble as shown in FIG. 3D. For example, atiming recovery error may cause the ending sync mark to be written late,thereby overwriting at least part of the previously written preambleleading to synchronization failure for both data sectors. Accordingly inone embodiment shown in FIG. 3E, instead of writing an ending sync marka gap may be left between the end of the newly written data sector 26and the previously written data sector 24 to ensure the previouslywritten preamble is not overwritten. In one embodiment, the gap shown inFIG. 3E may also facilitate overwriting data sector 22 by preventing anearly write (due to timing recovery error) from overwriting the end partof previously written data sector 26. That is, the gap enables a certaindegree of timing recovery jitter without overwriting part of apreviously written data sector. In one embodiment, when an ending syncmark is not written at the end of a write operation, the data sector maystill be synchronized when reading in the reverse direction using thetechniques described above, such as by using an intermediate sync markrecorded within the data sector (and erasing the intervening symbols),or performing reverse synchronization from an intervening or even thebeginning sync mark of the data sector.

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a data storage controller, orcertain operations described above may be performed by a read channeland others by a data storage controller. In one embodiment, the readchannel and data storage controller are implemented as separateintegrated circuits, and in an alternative embodiment they arefabricated into a single integrated circuit or system on a chip (SOC).In addition, the control circuitry may include a suitable preamp circuitimplemented as a separate integrated circuit, integrated into the readchannel or data storage controller circuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry. In someembodiments, at least some of the flow diagram blocks may be implementedusing analog circuitry (e.g., analog comparators, timers, etc.), and inother embodiments at least some of the blocks may be implemented usingdigital circuitry or a combination of analog/digital circuitry.

In addition, any suitable electronic device, such as computing devices,data server devices, media content storage devices, etc. may comprisethe storage media and/or control circuitry as described above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device configured to access amagnetic tape, the data storage device comprising: at least one headconfigured to access the magnetic tape; and control circuitry configuredto use the head to write contiguously to the magnetic tape a firstpreamble, followed by a first sync mark, followed by symbols of a firstdata sector, followed by a second sync mark, followed by a secondpreamble, followed by a third sync mark, followed by symbols of a seconddata sector.
 2. The data storage device as recited in claim 1, whereinthe data storage device comprises the magnetic tape.
 3. The data storagedevice as recited in claim 1, wherein: the magnetic tape is housed in acartridge assembly; and the data storage device comprises a tape driveassembly configured to receive the cartridge assembly.
 4. The datastorage device as recited in claim 1, wherein the control circuitry isfurther configured to: read the magnetic tape in a forward direction byreading the first sync mark in order to synchronize to the symbols ofthe first data sector; and read the magnetic tape in a reverse directionby reading the second sync mark in order to synchronize to the symbolsof the first data sector.
 5. The data storage device as recited in claim1, wherein the control circuitry is further configured to overwrite thesecond data sector with a third data sector by: overwriting at leastpart of the second preamble with a third preamble; overwriting at leastpart of the third sync mark with a fourth sync mark; and overwriting atleast part of the symbols of the second data sector with symbols of thethird data sector.
 6. The data storage device as recited in claim 5,wherein the control circuitry is further configured to read the magnetictape in a reverse direction by reading the third preamble and the secondsync mark in order to synchronize to the symbols of the first datasector.
 7. The data storage device as recited in claim 1, wherein thecontrol circuitry is further configured to overwrite the second datasector with a third data sector by overwriting at least part of thesecond sync mark with a third preamble used to synchronize timingrecovery when reading the third data sector.
 8. The data storage deviceas recited in claim 1, wherein the control circuitry is furtherconfigured to overwrite the first data sector with a third data sectorby overwriting at least part of the second sync mark with a third syncmark used to synchronize to symbols of the third data sector whenreading the third data sector in a reverse direction.
 9. The datastorage device as recited in claim 8, wherein the control circuitry isfurther configured to read the third data sector in the reversedirection by reading the second preamble in order to synchronize timingrecovery.
 10. The data storage device as recited in claim 1, wherein thecontrol circuitry is further configured to overwrite the first datasector with a third data sector by converting at least part of thesecond sync mark into a gap field separating an end of the third datasector from the second preamble.
 11. A data storage device configured toaccess a magnetic tape, the data storage device comprising: at least onehead configured to access the magnetic tape; and control circuitryconfigured to: use the head to continuously write a plurality of datasectors to the magnetic tape without leaving a gap between each datasector; and use the head to write contiguously to the magnetic tape afirst preamble, followed by a first sync mark, followed by symbols of afirst data sector, followed by a second sync mark, followed by a secondpreamble, followed by a third sync mark, followed by symbols of a seconddata sector.
 12. The data storage device as recited in claim 11, whereinthe data storage device comprises the magnetic tape.
 13. The datastorage device as recited in claim 11, wherein: the magnetic tape ishoused in a cartridge assembly; and the data storage device comprises atape drive assembly configured to receive the cartridge assembly. 14.The data storage device as recited in claim 11, wherein the controlcircuitry is further configured to: read the magnetic tape in a forwarddirection by reading the first sync mark in order to synchronize to thesymbols of the first data sector; and read the magnetic tape in areverse direction by reading the second sync mark in order tosynchronize to the symbols of the first data sector.
 15. The datastorage device as recited in claim 11, wherein the control circuitry isfurther configured to overwrite the second data sector with a third datasector by: overwriting at least part of the second preamble with a thirdpreamble; overwriting at least part of the third sync mark with a fourthsync mark; and overwriting at least part of the symbols of the seconddata sector with symbols of the third data sector.
 16. The data storagedevice as recited in claim 15, wherein the control circuitry is furtherconfigured to read the magnetic tape in a reverse direction by readingthe third preamble and the second sync mark in order to synchronize tothe symbols of the first data sector.
 17. The data storage device asrecited in claim 11, wherein the control circuitry is further configuredto overwrite the second data sector with a third data sector byoverwriting at least part of the second sync mark with a third preambleused to synchronize timing recovery when reading the third data sector.18. The data storage device as recited in claim 11, wherein the controlcircuitry is further configured to overwrite the first data sector witha third data sector by overwriting at least part of the second sync markwith a third sync mark used to synchronize to symbols of the third datasector when reading the third data sector in a reverse direction. 19.The data storage device as recited in claim 18, wherein the controlcircuitry is further configured to read the third data sector in thereverse direction by reading the second preamble in order to synchronizetiming recovery.
 20. The data storage device as recited in claim 11,wherein the control circuitry is further configured to overwrite thefirst data sector with a third data sector by converting at least partof the second sync mark into a gap field separating an end of the thirddata sector from the second preamble.
 21. A data storage devicecomprising: a magnetic tape; at least one head configured to access themagnetic tape; and a means for using the head to continuously write aplurality of data sectors to the magnetic tape without leaving a gapbetween each data sector, wherein the means for using the head tocontinuously write comprises a means for contiguously writing a firstpreamble, followed by a first sync mark, followed by symbols of a firstdata sector, followed by a second sync mark, followed by a secondpreamble, followed by a third sync mark, followed by symbols of a seconddata sector.
 22. The data storage device as recited in claim 21, furthercomprising: a means for reading the magnetic tape in a forward directionby reading the first sync mark in order to synchronize to the symbols ofthe first data sector; and a means for reading the magnetic tape in areverse direction by reading the second sync mark in order tosynchronize to the symbols of the first data sector.